Palladium and palladium alloys are known to be useful in a variety of industrial applications including the fabrication of jewelry, optical devices, electronic circuits and devices. Palladium and its alloys are attractive because of chemical inertness, surface luster, high electrical conductivity and excellent surface properties, particularly for electrical contacts. In many applications chemical inertness is highly advantageous for long life and high reliability. In addition, its high electrical conductivity makes palladium particularly useful in various electrical devices including electrical contacts such as are used in relays, switches and electrical contacts. Various palladium alloys such as palladium-silver are also useful for like applications. Indeed, because of the increasing cost of gold, palladium often appears more attractive economically as a contact material than is gold. For this reason, it is economically attractive to have an electroplating process for reliably plating ductile and adherent palladium to surfaces.
In particular, it is highly desirable to have an electroplating process which is highly reliable despite the possible introduction of foreign ions into the electroplating bath. It is also highly desirable to have a bath composition which permits reliable, efficient palladium plating even where foreign ions might be introduced into the plating bath. This is most critical in plating various types of electrical connectors and other electrical devices because of the possible introduction of copper ions into the plating bath.
Palladium electroplating processes and baths have been described in a number of references including: U.S. Pat. No. 1,970,950 issued to E. M. Wise on Aug. 21, 1934; U.S. Pat. No. 1,993,623 issued to A. R. Raper on Mar. 5, 1935; U.S. Pat. No. 1,981,715 issued to R. H. Atkinson on Nov. 20, 1934; U.S. Pat. No. 3,920,526 issued to J. J. Caricchio, Jr. et al on Nov. 18, 1975; U.S. Pat. No. 1,921,941 issued to A. R. Powell et al on Aug. 8, 1933; U.S. Pat. No. 3,544,435 issued to H. C. Angus et al on Dec. 1, 1970; U.S. Pat. No. 3,458,409 issued to S. Hayashi et al on July 29, 1969; U.S. Pat. No. 2,452,308 issued to G. C. Lambros on Oct. 26, 1948; and U.S. Pat. No. 3,150,065 issued to G. D. Fatzer on Sept. 22, 1964.